[Qemu-devel] [PATCH 1/2] tcg-x86_64: Special-case all 32-bit AND operands.

[Richard Henderson]

This avoids an unnecessary REX.W prefix when dealing with AND
operands that fit into a 32-bit quantity.  The most common change
actually seen is movz[wb]q -> movz[wb]l.

Similarly, avoid REXW in ext{8,16}u_i64 tcg opcodes.

Signed-off-by: Richard Henderson <address@hidden>
---
 tcg/x86_64/tcg-target.c |   26 ++++++++------------------
 1 files changed, 8 insertions(+), 18 deletions(-)

diff --git a/tcg/x86_64/tcg-target.c b/tcg/x86_64/tcg-target.c
index 2339091..f584c94 100644
--- a/tcg/x86_64/tcg-target.c
+++ b/tcg/x86_64/tcg-target.c
@@ -426,24 +426,18 @@ static inline void tgen_arithi64(TCGContext *s, int c, 
int r0, int64_t val)
     } else if ((c == ARITH_ADD && val == -1) || (c == ARITH_SUB && val == 1)) {
         /* dec */
         tcg_out_modrm(s, 0xff | P_REXW, 1, r0);
-    } else if (val == (int8_t)val) {
-        tcg_out_modrm(s, 0x83 | P_REXW, c, r0);
-        tcg_out8(s, val);
-    } else if (c == ARITH_AND && val == 0xffu) {
-        /* movzbl */
-        tcg_out_modrm(s, 0xb6 | P_EXT | P_REXW, r0, r0);
-    } else if (c == ARITH_AND && val == 0xffffu) {
-        /* movzwl */
-        tcg_out_modrm(s, 0xb7 | P_EXT | P_REXW, r0, r0);
     } else if (c == ARITH_AND && val == 0xffffffffu) {
         /* 32-bit mov zero extends */
         tcg_out_modrm(s, 0x8b, r0, r0);
+    } else if (c == ARITH_AND && (uint64_t)val <= 0xffffffffu) {
+        /* AND with no high bits set can use a 32-bit operation.  */
+        tgen_arithi32(s, c, r0, val);
+    } else if (val == (int8_t)val) {
+        tcg_out_modrm(s, 0x83 | P_REXW, c, r0);
+        tcg_out8(s, val);
     } else if (val == (int32_t)val) {
         tcg_out_modrm(s, 0x81 | P_REXW, c, r0);
         tcg_out32(s, val);
-    } else if (c == ARITH_AND && val == (uint32_t)val) {
-        tcg_out_modrm(s, 0x81, c, r0);
-        tcg_out32(s, val);
     } else {
         tcg_abort();
     }
@@ -1182,16 +1176,12 @@ static inline void tcg_out_op(TCGContext *s, int opc, 
const TCGArg *args,
         tcg_out_modrm(s, 0x63 | P_REXW, args[0], args[1]);
         break;
     case INDEX_op_ext8u_i32:
+    case INDEX_op_ext8u_i64:
         tcg_out_modrm(s, 0xb6 | P_EXT | P_REXB, args[0], args[1]);
         break;
     case INDEX_op_ext16u_i32:
-        tcg_out_modrm(s, 0xb7 | P_EXT, args[0], args[1]);
-        break;
-    case INDEX_op_ext8u_i64:
-        tcg_out_modrm(s, 0xb6 | P_EXT | P_REXW, args[0], args[1]);
-        break;
     case INDEX_op_ext16u_i64:
-        tcg_out_modrm(s, 0xb7 | P_EXT | P_REXW, args[0], args[1]);
+        tcg_out_modrm(s, 0xb7 | P_EXT, args[0], args[1]);
         break;
     case INDEX_op_ext32u_i64:
         tcg_out_modrm(s, 0x8b, args[0], args[1]);
-- 
1.6.5.2